Width (feet)
72
0
1.0
1.0
47 knots
1.
72
0.5
0.5
36
36
0
0
0
25
50
75
100
125
150
175
200
Length (feet)
225
250
275
300
325
350
375
Figure 3—Drop pattern characteristics for the Griffith 100-gallon helibucket with an airspeed of 47 knots and a drop height
of 42 feet. The contour lines are at coverage levels of 0.5, 1, 2, 3, 4, 6, 8, and 10 gallons per 100 square feet.
Width (feet)
72
72
60 knots
36
36
0.5
5
0.
0.5
1.0
0
0
0
25
50
75
100
125
150
175
200
225
250
275
300
325
350
375
Length (feet)
Figure 4—Drop pattern characteristics for the Griffith 100-gallon helibucket with an airspeed of 60 knots and a drop
height of 64 feet. The contour lines are at coverage levels of 0.5, 1, 2, 3, 4, 6, 8, and 10 gallons per 100 square feet.
4
Effect of Airspeed on Length of Line at Various Coverage Levels
Effect of Airspeed on Length of Line at Various Coverage Levels
100-Gallon Griffith Bucket Using Gum-Thickened Retardant
100-Gallon Griffith Bucket Using Water
230
230
184
CL=0.5
CL=1
CL=2
138
CL = Coverage Level
Length of Line (feet)
Length of Line (feet)
184
CL = Coverage Level
92
46
138
92
46
0
30
35
40
45
50
55
60
Air Speed (knots)
Effect of Airspeed on Length of Line at Various Coverage Levels
230
100-Gallon Griffith Bucket Using Foam
184
CL = 0.5
CL = 1
CL = 2
CL = 3
138
CL = Coverage Level
92
46
0
30
35
40
45
0
30
35
40
45
50
55
60
Air Speed (knots)
Figure 5—Use this graph to estimate the speed needed to produce the
longest line of water at various coverage levels.
Length of Line (feet)
CL = 0.5
CL = 1
CL = 2
CL = 3
50
55
60
Figure 7—Use this graph to estimate the speed needed to produce the
longest line of gum-thickened retardant at various coverage
To select the proper helicopter speed, use
Table 1 to determine the coverage level
required by the NFDRS or Fire Behavior
Fuel Model. The coverage levels in Table
1 represent the coverage level required for
the average fire intensity for each fuel
model. The required coverage level can be
adjusted up or down depending on the
actual fire intensity. Once the required
coverage level is determined, the airspeed
can be found. Use the graph for the
material dropped (water, foam, or gumthickened retardant) to find the speed that
produces the longest line for the desired
coverage level. The same information can
be found in the appropriate drop table.
Air Speed (knots)
Figure 6—Use this graph to estimate the speed needed to produce the
longest line of foam at various coverage levels.
For example, if a fire is burning in NFDRS
Fuel Model C (Fire Behavior Model 2),
represented by conifer with grass, Table 1
shows that a coverage level of 2 is
required. The graph for water shows that
for coverage level 2, an airspeed of about
36 knots produces the longest line.
The ground drop characteristics for the
Griffith 100-gallon helibucket were
derived through controlled drop test
procedures on flat ground (Figure 8). This
information is to serve only as a guide in
assisting field personnel to determine the
proper drop height and airspeed for
delivering water, foam, or gum-thickened
retardant. Actual coverage may vary
depending on terrain, wind, weather, and
pilot proficiency.
5
About the Author…
Ann Suter is a statistician working with
the Wildland Fire Chemical Systems
Group. She has a master’s degree in
International Development from the
American University. She worked to
control soil erosion in Jamaica as a Peace
Corps Volunteer before joining the Forest
Service in 1997.
Figure 8
75%
4 7/8 x 5 7/8
Original Photo 6 1/2 x 9 7/8
Additional single copies of this
document may be ordered from:
USDA Forest Service
Missoula Technology and
Development Center
Building 1, Fort Missoula
Missoula, MT 59804-7294
Phone: (406) 329-3978
Fax: (406) 329-3719
For additional technical information,
contact Ann Suter or Paul Solarz at
the address above.
Ann Suter
Phone: (406) 329-4719
Fax: (406) 329-4811
Internet: asuter@fs.fed.us
Lotus Notes: Ann Suter/WO/USDAFS
Paul Solarz
Phone: (406) 329-4719
Fax: (406) 329-4811
Internet: psolarz@fs.fed.us
Lotus Notes: Paul Solarz/WO/USDAFS
An electronic copy of this document is
available on the Forest Service’s
FSWeb Intranet at:
http://fsweb.mtdc.wo.fs.fed.us
Print to Outside Edge of Borders
No Not Print Borders
Figure 8—Drop test of the Griffith 100-gallon helibucket.
The Forest Service, United States Department of Agriculture, has
developed this information for the guidance of its employees, its
contractors, and its cooperating Federal and State agencies, and is
not responsible for the interpretation or use of this information by
anyone except its own employees. The use of trade, firm, or corporation
names in this publication is for the information and convenience of
the reader, and does not constitute an endorsement by the Department
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USDA is an equal opportunity provider and employer.
6